* Remove pre-3.6 server versions from Evergreen matrix
* Remove skipped tests for pre-3.6 servers
* Remove old mongo-orchestration configs and Evergreen tasks
* Remove flaky replica set tests
These tests assume a particular replica set member is always the primary, so tag assertions may fail if a different member is elected. The server-getTags-002.phpt test has more flexible assertions for replica set tags, so we can safely remove these tests.
* Bump libmongoc to 1.19-dev
* PHPC-1890: Constant for ReadConcern snapshot level
* Move Manager::startSession() error test and delete obsolete test
The deleted error test was redundant. It was originally created in ca4c52eb1c to work around changes in PHP 8, but 60febd0f28 subsequently reintroduced a portable version of the test case.
Also adds missing SKIPIF to startSession test.
* PHPC-1889: Session snapshot option
* PHPC-1875: Session with snapshot=true cannot perform writes
* PHPC-1876: Session with snapshot=true requires MongoDB 5.0+
